The stock was downgraded to 'neutral' by Credit Suisse. Plus, Even though the DOJ approved the merger, the FCC is still evaluating. While this is happening, Sirius' debt has climbed well into the $Billion threshold. Refinancing $Billion dollars of debt will be tough even in a good market. I would think the latter issue alone is enough to drive the price down.
warning: i'm a beginner investor and may have some concepts twisted. hope this helps.
Unfortunately, the real is "it depends".
optimistic (bullish): you could see this as the stock being on sale and load up.
pessimistic (bearish): you could see this as there being too much debt and even if the price goes back up, it will be a while and it will definitely be slow (even after the merger).
There is a strong myth that mergers automatically mean things will get better. Thats not necessarily true. In this case, both companies have substantial debt and substantial technical issues to work out after the merge. There are tons of articles that outline all the hurdles that await the new company (if approved). My advice is to read a few fact-based articles (not an article written from a speculative analyst).
Personally, I made a decision to sell and focus on the securities that are moving today. If the merger happens and its a good deal, I'll jump in. I figure a good deal, will probably still be a good deal when I get there. I once thought Google was too expensive at $70. It was still good deal!
hope this helps and good luck on your decision!